1. Field of the Invention
The present invention relates to a reduced-pressure drying unit and a coating film forming method for vaporizing a solvent from a coating solution when the coating solution made by, for example, mixing a component of a coating film in the solvent, for example, a resist solution is applied to a substrate such as a semiconductor wafer or an LCD substrate (a glass substrate for a liquid crystal display) to form the coating film.
2. Description of the Related Art
In fabrication processes of semiconductor devices and LCDs, resist processing is performed for a substrate to be processed by a technique called photolithography. This technique includes a series of steps of applying a resist solution to, for example, a semiconductor wafer (hereinafter, referred to as a wafer) to form a solution film on its front face, exposing the resist film to light using a photomask, and thereafter performing a developing treatment to obtain a desired pattern.
There is one method for the above-described coating treatment of the resist solution, in which, for example, as shown in FIG. 30, a coating solution is applied in a manner of so-called drawing with one stroke such that the coating solution (the resist solution) made by mixing a resist that is a component of a coating film and a solvent is discharged onto a wafer front face from a nozzle 10 while the nozzle 10 provided above the wafer W is being reciprocated in an X-direction and the wafer W is intermittently moved in a Y-direction. Numeral 12 in FIG. 30 denotes a mask which covers a region other than a circuit formation region 11 of the wafer.
For carrying out the above-described method, it is considered to be preferable that the wafer is carried into a reduced-pressure drying unit for reduced-pressure drying immediately after the coating solution is applied onto the wafer because a solvent having a low vaporization is used as the solvent contained in the coating solution and the uniformity of the film thickness of the coating film is secured by quickly removing the solvent from the front face of the wafer.
FIG. 31 is a view showing a conventional reduced-pressure drying unit in which numeral 13 denotes a hermetic container constituted by a lid body 14 and a mount 15, and a ceiling portion of the lid body 14 is formed with an opening 14a. The opening 14a can communicate with a vacuum pump 16 through an exhaust pipe 14b to reduce the pressure in the hermetic container 13. In such a unit, the wafer W is mounted on the mount 15 and heated by a not shown heater, and the vacuum pump 16 is actuated to reduce the pressure in the hermetic container 13, thereby causing the solvent, for example, a thinner or the like remaining on the front face of the wafer W to vaporize (dry) and the vaporized solvent to be sucked toward the vacuum pump 16 side, so that the resist component in the coating solution remains on the front face of the wafer W.
Meanwhile, a coating solution 17 on the front face of the wafer, when carried into the reduced-pressure drying unit, is rounded, for example, as shown in FIG. 32, at a peripheral region of the wafer (a region inside by a predetermined distance, for example, about 20 mm from the periphery) due to a surface tension of the coasting solution itself. Therefore, it is considered to provide a current plate 18 above the wafer W mounted on the mount 15 in such a manner that the current plate 18 faces the wafer W as shown by a dotted line in FIG. 31. When the current plate 18 is provided as described above and the pressure in the hermetic container 13 is reduced, an air current is formed which spreads outward between the current plate 18 and the wafer W to cause the coating solution to spread toward the periphery on the front face of the wafer.
Therefore, if the current plate 18 is provided and reduced-pressure drying processing is performed, the coating solution is drawn toward the periphery as shown in FIG. 33, resulting in an extremely large thickness of the coating film at the peripheral region. The coating film with a rounded shape or an accumulated portion at the peripheral region as described above cannot be used as a circuit formation region because the peripheral region of the coating film is greatly different in film thickness from the center region. Hence, there is a request that the circuit formation region occupies an area as large as possible to improve the yield of chips per wafer, and thus a significant problem is a control of the film thicknesses at the center region and the peripheral region in the coating film formed on the front face of the wafer.
The present invention is made due to such circumstances, and it is an object of the present invention to provide a technique capable of securing a high in-plane uniformity of film thickness by controlling the film thickness of a coating film during reduced-pressure drying in a reduced-pressure drying unit for a substrate provided, for example, in a coating film forming apparatus.
In order to attain the above object, according to a first aspect of the present invention, a reduced-pressure drying unit of the present invention comprises: a hermetic container provided therein with a mount for mounting thereon a substrate coated with a coating solution made by mixing a component of a coating film and a solvent; a vacuum exhauster connected to the hermetic container through an exhaust passage for reducing a pressure in the hermetic container to vaporize the solvent from the coating solution on the substrate; a current member provided to face a front face of the substrate mounted on the mount; and a current member raising and lowering mechanism for raising and lowering the current member, wherein the current member is raised and lowered by the current member raising and lowering mechanism to change in height position while the pressure inside the hermetic container is reduced to vaporize the solvent from the coating solution on the substrate.
According to another aspect, a reduced-pressure drying unit of the present invention comprises: a hermetic container provided therein with a mount for mounting thereon a substrate coated with a coating solution made by mixing a component of a coating film and a solvent; a heater provided in the mount for heating the substrate; a vacuum exhauster connected to the hermetic container through an exhaust passage for reducing a pressure in the hermetic container to vaporize the solvent from the coating solution on the substrate; and an annular member made of a material having a heat conductivity different from that of the mount, provided on the mount and coming into contact with a peripheral region of a rear face of the substrate.
According to still another aspect, a reduced-pressure drying unit of the present invention comprises: a hermetic container provided therein with a mount for mounting thereon a substrate coated with a coating solution made by mixing a component of a coating film and a solvent; a vacuum exhauster connected to the hermetic container through an exhaust passage for reducing a pressure in the hermetic container to vaporize the solvent from the coating solution on the substrate; and a plurality of aligning members provided at positions outside the mount and apart from a center position of the mount by equal distances in radial directions, wherein the plurality of aligning members synchronously move in substantially horizontal directions from the positions outside the substrate to positions to come into contact with an edge of the substrate to align the center position of the mount and a center position of the substrate.
According to yet another aspect, a reduced-pressure drying unit of the present invention comprises: a hermetic container provided therein with a mount for mounting thereon a substrate coated with a coating solution made by mixing a component of a coating film and a solvent; a vacuum exhauster connected to the hermetic container through an exhaust passage for reducing a pressure in the hermetic container to vaporize the solvent from the coating solution on the substrate; a supporting member provided at the mount for supporting the substrate while slightly lifting the substrate from a front face of the mount; and a ventilation passage formed in the mount and communicating with an outside of the hermetic container.
According to still another aspect, the present invention is a method for forming a coating film on a substrate which comprises: a step of applying to a front face of the substrate a coating solution made by mixing a component of a coating film and a solvent; a step of mounting the substrate coated with the coating solution in a hermetic container; a reduced-pressure drying step of reducing a pressure in the hermetic container by exhausting an air therein by a vacuum exhauster to vaporize the solvent in the coating solution applied on the substrate; a first step, performed in the reduced-pressure drying step, of positioning a current member so that the current member faces the substrate at a first position above the substrate mounted in the hermetic container; and a second step, performed in the reduced-pressure drying step and after the first step, of moving the current member so that the current member faces the substrate at a second position different from the first position.
According to still another aspect, the present invention is a method for forming a coating film on a substrate which comprises: a step of applying to a front face of the substrate a coating solution made by mixing a component of a coating film and a solvent; a step of mounting the substrate coated with the coating solution on a top face of a mount in a hermetic container; subsequently, a step of aligning center positions of the substrate and the mount by an aligning member; and a reduced-pressure drying step of reducing a pressure in the hermetic container by exhausting an air therein by a vacuum exhauster to vaporize the solvent in the coating solution applied on the substrate.
According to the present invention, an exhaust current flowing outward from the center is formed between the current member and the substrate during the reduced-pressure drying processing, but the liquid flow of the coating solution on the substrate is controlled by changing the height position of the current member in the reduced-pressure drying processing, thereby controlling the film thickness of the coating film on the front face of the substrate. This prevents a rounded shape or an accumulated portion of the coating solution at a peripheral region of the substrate, so that the film thicknesses of the coating solution are made uniform between the center region and the peripheral region, resulting in improved uniformity of film thickness.
Further, according to the present invention, the substrate is heated by the heater provided in the mount, but the peripheral region of the substrate is in contact with the annular member which has a heat conductivity different from that of the mount, thereby causing different temperatures and accordingly different vaporization rates of the solvent contained in the coating solution between the center region and the peripheral region of the substrate. Consequently, it is possible to control the film thickness of the coating film on the front face of the substrate, so that the film thicknesses of the coating solution are made uniform between the center region and the peripheral region, resulting in improved uniformity of film thickness.
Further, according to the present invention, the substrate can be mounted on the mount with the center of the mount and the center of the substrate aligned with each other, so that uniform reduced-pressure drying processing can be performed.
Furthermore, according to the present invention, when the hermetic container is returned from the reduced-pressure atmosphere to the atmospheric pressure, the reduced-pressure state is quickly released also on the rear face side of the substrate mounted on the mount because of air leakage from the ventilation passage, thereby preventing the center portion of the rear face side of the substrate from being sucked to the mount for prevention of warpage of the substrate.